Based on the rationale that CuET impairs UPS outside the proteasome we addressed here its toxic effect using the recently described clinically-relevant BTZ-resistant form of MM mutated in the proteasomal subunit PSMB5, responsible for resistance to BTZ and its derivates Ixazomib (IXA) and Carfilzomib (CARF) [4]. Here, PSMB5 is linked to Miyoshi myopathy.